Recent cellular phone designs and features desired by the consuming market are driving demand for better high audio speaker low end frequency performance. In the past, much of the audio speaker performance and design was driven primarily by a voice centric device. Current phone designs fail to adequately compensate for the new multimedia capabilities found in phones which continue to be designed primarily around voice centric specifications. Further aggravating or complicating the demand for better high audio speaker low end frequency performance is the trend of phones getting smaller resulting in smaller high audio speaker back cavity volumes. As the speaker back cavity volumes reduce, the speakers resonant frequency raises and low frequency performance is degraded. With phones getting smaller, maintaining the low end frequency performance presently achieved in prior larger phones (whether the phone is used for multimedia or not) presents a greater challenge for designers.
Some applications are implementing different size battery doors to enlarge the loud speaker back volume. When the back cavity size changes, the bass reflex frequency will change, unless something else changes to compensate. Bass reflex theory is found in many textbooks and products such as standard non-portable speakers that do not have replaceable housings. Such existing devices do not need to contend with implementing a variability of parameters to maintain an appropriate bass reflex effect at a specific frequency. Certainly, base reflex theory has not been applied to high audio loud speakers in cellular phones and other portable electronic devices where the speaker back volumes can vary based on alternate replaceable housing configurations.